404 STUDIES FOR STUDENTS 



Iron sulphide. — Troilite-pyrrhotite . — The exact form and com- 

 position of the iron sulphide which is a common ingredient in 

 meteorites is a question not yet satisfactorily answered. For 

 convenience, Rose's assumption that the iron sulphide of iron 

 meteorites is troilite, that of stone meteorites pyrrhotite, is 

 usually followed, but there are many occurrences which do not 

 harmonize with this view. 



The iron sulphide known as troilite is usually found massive, 

 though crystals have been observed which have been referred by 

 Brezina to the hexagonal and by Linck to the isometric system. 

 The color varies from bronze-yellow to tomback-brown. Streak 

 black. Hardness, 4. Specific gravity, 4.68-4.82. Generally 

 found to be non-magnetic, although magnetic troilite has been 

 reported. Cohen suggests that the magnetism may be due to 

 included nickel-iron. The mineral fuses in the reducing flame 

 to a black, magnetic globule. Decomposed by hydrochloric 

 acid with evolution of hydrogen sulphide, but without separation 

 of sulphur. Not affected by copper sulphate or fuming nitric 

 acid. These reagents may be used, therefore, for its separation. 



Most analyses show a composition approximating very 

 closely to FeS. Meunier, however, obtained results more 

 nearly in accord with the formula Fe^^S^g. As this is the com- 

 position of pyrrhotite he regards the two as identical. The 

 specific gravities which he obtained, however, correspond to 

 those observed by others for troilite, and there seems therefore, 

 some reason to doubt the correctness of his analysis. 



Troilite is almost universally present in the iron meteorites. 

 It may be very unequally distributed in a single mass, however, 

 being abundant in some portions and lacking in others. It 

 usually occurs in the form of nodules, but also as plates and 

 lamellae. The nodules vary greatly in shape and size. Rounded 

 and oval forms are common, as are also lens and dumb-bell 

 shapes. In Carlton a star-like form occurs. Smith separated 

 from the Cosby's Creek iron a nodule weighing 200 grams, 

 while one from the Magura iron measured 1 3^^™ in diameter. 

 When troilite occurs as lamellae, these are often regularly 



